CD4 and COVID-19: As expected, the two MSCs clone significantly inhibited CD4 + T cells from PBMC of COVID-19 patients to differentiate into Th1 and Th17 subpopulation and promoted the maturation of Tregs subpopulation in PBMCs induced by IL-2 (Fig. 4e, S3), whereas there is no immunomodulatory effects for SARS-CoV-2 mAbs treatment alone.